This invention relates to a scroll member used with a scroll type liquid pump, a scroll type compressor, a scroll type expander, etc.
The principle of operation of a scroll type pump, compressor or expander is described in, for example, U.S. Pat. No. 801,182.
A scroll type fluid apparatus comprises two scroll members each including an end plate and a wrap of the vortical form located in an upstanding position on the surface of the wrap, with the two scroll members being arranged in combination in such a manner that the end plates face each other at their surfaces and the wraps are in meshing engagement with each other so that one of the scroll members moves in orbiting movement while being prevented from rotating on its own axis with respect to the other scroll member. Thus, the pockets defined between the two scroll members have their volumes varied as one scroll member moves in orbiting movement while the other scroll member remains stationary.
The curve constituting the wrap of each scroll member is in the majority of its length an involute curve of a circle. Such curve is shown, for example in U.S. Pat. Nos. 801,182, 3,600,114, 3,817,664, and 3,994,635. There is nowhere in the prior art documents, however, any description of the shape of the starting end portion of the wrap.
Additionally U.S. Pat. No. 3,994,635 discloses a method of producing a scroll member wherein an end plate and a wrap are made separately and the wrap is fitted into a shallow groove formed in the end plate. It is also disclosed therein that milling is relied on for forming the shallow groove on the end plate. It will be understood from this that the scroll member can be produced by milling. However, there is no express mention in this prior art document of a method for forming the scroll member in a concrete manner.